Bulk superconductivity at 14 K in single crystals of Fe1+y Tex Se1-x

Resistivity, magnetic susceptibility, and heat-capacity measurements are reported for single crystals of Fe1+y Tex S-x grown via a modified Bridgeman method with 0<y<0.15 and x=1, 0.9, 0.75, 0. 67, 0.55, and 0.5. Although resistivity measurements show traces of superconductivity near 14 K for all x except x=1, only crystals grown with compositions near x=0.5 exhibit bulk superconductivity. The appearance of bulk superconductivity correlates with a reduction in the magnitude of the magnetic susceptibility at room temperature and smaller values of y, the concentration of Fe in the Fe(2) site.